1. Field of the Invention
The present invention relates generally to a method of fabricating a semiconductor device such as LSI (large-scale integrated circuit), and more particularly, to a method for disposing metal wiring on the surface of an insulating film formed on a semiconductor substrate.
2. Description of Related Art
In the steps of fabricating a semiconductor device such as LSI, a so-called damascene process may, in some cases, be used in order to form a metal wiring pattern on the surface of an insulating film formed on a semiconductor substrate.
FIGS. 8A to 8G are cross-sectional views showing the steps of forming a metal wiring pattern by a conventional damascene process. As shown in FIG. 8A, an insulating film 92 composed of SiO2 (silicon dioxide) is formed on a semiconductor substrate 91. As shown in FIG. 8B, a recess 93 for embedding metal wiring is formed by using a photolithography technique in a portion, corresponding to a region where metal wiring should be formed, on the surface of the insulating film 92.
Thereafter, as shown in FIG. 8C, a barrier metal film 94 composed of TiN (titanium nitride), for example, is formed on the insulating film 92 having the recess 93 formed therein. Further, as shown in FIG. 8D, a seed film 95 composed of a metal such as Cu (copper) is formed on the barrier metal film 94. As shown in FIG. 8E, the seed film 95 is subjected to electroplating using a metal of the same type as that composing the seed film 95, to form a metal wiring film 96.
CMP (Chemical Mechanical Polishing) processing is then performed, so that the metal wiring film 96, the seed film 95, and the barrier metal film 94 on the insulating film 92 are successively ground away, as shown in FIGS. 8E to 8G. All the metal wiring film 96, the seed film 95, and the barrier metal film 94, which are laminated on a surface area 92a outside the recess 93 in the insulating film 92, are ground away, so that the whole of the surface area 92a is exposed. The CMP processing is then terminated. Consequently, the pattern of metal wiring 97, which has been embedded in the recess 93, is formed on the surface of the insulating film 92.
In the above-mentioned conventional method, however, the surface, outside the recess 93, of the insulating film 92 and the surface of the metal wiring 97 are not flush with each other, and the surface of the metal wiring 97 becomes depressed in a dish shape in cross-sectional view, that is, so-called dishing occurs, as shown in FIG. 8G, at the time when the CMP processing is terminated.
The foregoing will be described in detail. If the metal wiring film 96 is formed on the seed film 95 by electroplating, a depression occurs in a portion, opposite to the recess 93 in the insulating film 92, on the surface of the metal wiring film 96, as shown in FIG. 8E. A surface plate pad used in CMP processing thereafter performed is composed of a material having flexibility, for example, foamed polyurethane. Therefore, the surface plate pad is deformed in a shape along the inequality in the surface of the metal wiring film 96, to polish the whole surface of the metal wiring film 96 almost uniformly. Consequently, the surface of the metal wiring film 96 is ground away in a state where the portion, opposite to the recess 93 in the insulating film 92, is depressed. At the time point where the surface of the metal wiring film 96 in the recess 93 is almost flush with the surface, outside the recess 93, of the insulating film 92, therefore, the metal wiring film 96, the seed film 95, and the barriermetal film 94 remain on the surface area 92a, as shown in FIG. 8F.
When the CMP processing is continued in order to remove the metal wiring film 96, the seed film 95, and the barrier metal film 94 which remain on the surface area 92a, the metal wiring film 96 in the recess 93 is gradually ground away. In the CMP processing, the metal wiring film 96 composed of a metal material such as Cu is ground away more easily than the barrier metal film 94 composed of TiN, for example. Therefore, after the barrier metal film 94 is exposed in the surface area 92a, the polishing rate of an area of the metal wiring film 96 in the recess 93 is higher than that in an area of the barrier metal film 94 on the surface area 92a. As a result, at the time point where the whole surface area 92a is exposed, the metal wiring 97, which is embedded in the recess 93, is dished.
By the dishing of the metal wiring 97, the cross-sectional area of the metal wiring 97 is smaller than its designed or desired value. As a result, the electrical resistance of the metal wiring 97 is larger than its designed or desired value.
In a case where multi-layer wiring is formed on a semiconductor substrate, if the metal wiring 97 is dished, the subsequent steps are adversely affected. In a case where the metal wiring 97 is dished, for example, when a further silicon dioxide insulating film is formed on the insulating film 92 in which the metal wiring 97 has been embedded, a portion, opposite to the metal wiring 97, on the surface of the further silicon dioxide insulating film becomes depressed, resulting in defocusing at the exposure process in a photolithographic process for patterning the further insulating film with a recess for embedding a further metal wiring. After a metal wiring film is formed on the further silicon dioxide insulating film, CMP processing is performed in order to remove an unnecessary portion, outside the recess, of the metal wiring film. However, the metal wiring film disadvantageously remains in a depression occurring in the further silicon dioxide insulating film. Therefore, the further metal wiring thus formed may be short-circuited by the remaining metal wiring film.
As a method of avoiding such a problem, it is considered that the photolithographic process is carried out after the surface of the further silicon dioxide insulating film is flattened. However, this method is not preferable because the number of steps is increased, thereby increasing the fabrication cost.
An object of the present invention is to provide a method of fabricating a semiconductor device, in which metal wiring can be prevented from being dished.
In order to attain the above-mentioned object, a first aspect of the present invention is directed to a method of fabricating a semiconductor device by disposing metal wiring on the surface of an insulating film formed on a semiconductor substrate, comprising the steps of forming a recess in the insulating film; laminating a metal wiring film composed of a metal wiring material on the insulating film having the recess formed therein; selectively removing the metal wiring film laminated on a surface area outside the recess in the insulating film; and polishing the metal wiring film laminated above the recess by chemical mechanical polishing after selectively removing the metal wiring film.
It is preferable that the step of polishing the metal wiring film by the chemical mechanical polishing is continued until the surface of the metal wiring film and the surface, outside the recess, of the insulating film are almost flush with each other.
According to the present invention, the metal wiring film on the surface area outside the recess in the insulating film is removed before processing using the chemical mechanical polishing is performed. Therefore, the chemical mechanical polishing processing for removing an unnecessary portion of the metal wiring film can be terminated at the time point where the surface of the metal wiring film is flush with the surface, outside the recess, of the insulating film. Consequently, the metal wiring embedded in the recess in the insulating film can be prevented from being dished.
Consequently, it is possible to obtain good-quality metal wiring having a cross-sectional area and an electrical resistance which are equal to their designed or desired values.
The surface of the insulated film and the surface of the metal wiring can be made almost flush with each other. When the method according to the present invention is applied to formation of multi-layer wiring, therefore, a new insulating film can be formed so as to be nearly flat on the insulating film and the metal wiring. Accordingly, it is possible to prevent defocusing at the exposure processing in a photolithographic process for patterning a further insulating film with a recess for embedding a further metal wiring. Further, it is possible to prevent the further metal wiring from being short-circuited by the metal wiring film remaining in a depression occurring in the further insulating film. Moreover, processing for flattening the further insulating film need not be additionally performed in order to prevent the defocusing and the short-circuit of the further metal wiring. Consequently, the fabrication cost is not increased.
It is preferable that the step of selectively removing the metal wiring film comprises the step of selectively forming a patterning mask in a region, opposite to the recess, on the surface of the metal wiring film, and the step of selectively removing a portion, other than a portion masked by the patterning mask, of the metal wiring film.
It is preferable that the portion, other than the portion masked by the patterning mask, of the metal wiring film is removed by etching.
According to the method, the metal wiring film on the surface area outside the recess in the insulating film can be removed by forming the patterning mask in the region, opposite to the recess, on the surface of the metal wiring film and then, etching the portion other than the portion masked by the patterning mask, for example.
It is preferable that the step of laminating a barrier metal film on the insulating film having the recess formed therein is further included between the step of forming the recess and the step of laminating the metal wiring film. In this case, it is preferable that the barrier metal film laminated on the surface area outside the recess in the insulating film is also selectively removed in the step of selectively removing the metal wiring film.
The barrier metal film is composed of Ti (titanium), TiN (titanium nitride), etc. In the chemical mechanical polishing, the barrier metal film is ground away less easily than a metal wiring film composed of a metal material such as Cu (copper). When the barrier metal film laminated on the surface area outside the recess in the insulating film, together with the metal wiring film, is polished in the chemical mechanical polishing processing, therefore, the polishing rate of the metal wiring film is higher than that of the barrier metal film. Therefore, the metal wiring film is ground away extra. As a result, the metal wiring is dished.
Therefore, the barrier metal film laminated on the surface area outside the recess in the insulating film, together with the metal wiring film laminated on the surface area outside the recess in the insulating film, is removed before the chemical mechanical polishing processing is performed. At the time of the chemical mechanical polishing processing, therefore, the metal wiring film is prevented from being excessively polished in order to remove the barrier metal film. Even in a case where the barrier metal film is formed, therefore, the metal wiring can be prevented from being dished.
A second aspect of the present invention is directed to a method of fabricating a semiconductor device by disposing metal wiring on the surface of an insulating film formed on a semiconductor substrate, comprising the steps of forming a recess in the insulating film; laminating a barrier metal film on the insulating film having the recess formed therein; selectively removing a portion, outside the recess, of the barrier metal film; depositing a metal wiring film composed of a metal wiring material on the barrier metal film remaining in the depression after removing the barrier metal film; and polishing the metal wiring film by chemical mechanical polishing.
According to the present invention, the portion, outside the recess, of the barrier metal film is removed prior to forming the metal wiring film. At the time of processing using the chemical mechanical polishing for removing an unnecessary portion of the metal wiring film, therefore, the metal wiring film is prevented from being excessively polished in order to remove the barrier metal film. Accordingly, it is possible to satisfactorily prevent the metal wiring from being dished.
Consequently, it is possible to obtain good-quality metal wiring having a cross-sectional area and an electrical resistance which are equal to their designed or desired values.
The step of polishing the metal wiring film by the chemical mechanical polishing is terminated at the time point where a surface, outside the recess, of the insulating film is exposed. Accordingly, a surface, inside the recess, of the metal wiring film and the surface, outside the recess, of the insulating film can be made almost flush with each other.
When the method according to the present invention is applied to formation of multi-layer wiring, therefore, a further insulating film can be formed so as to be nearly flat on the insulating film and the metal wiring. Accordingly, it is possible to prevent defocusing at the exposure processing in a photolithographic process for patterning the further insulating film with a recess for embedding a further metal wiring. Further, it is possible to prevent the further metal wiring from being short-circuited by the metal wiring film remaining in a depression occurring in the further insulating film. Moreover, processing for flattening the further insulating film need not be additionally performed in order to prevent the defocusing and the short-circuit of the metal wiring. Accordingly, the fabrication cost is not increased.
The metal wiring film may be formed on only the barrier metal film remaining inside the recess, or may be formed on both the surface, outside the recess, of the insulating film and on the barrier metal film remaining inside the recess.
It is preferable that the step of depositing the metal wiring film comprises the step of forming a seed film composed of a metal wiring material by sputtering on the barrier metal film remaining inside the recess, and the step of subjecting the seed film to electroplating using the metal wiring material.
Furthermore, in the step of selectively removing the barrier metal film, the portion, outside the recess, of the barrier metal film may be removed by the chemical mechanical polishing, or may be removed by forming a patterning mask for selectively covering a surface, inside the recess, of the barrier metal film and then, selectively etching a portion, other than a portion masked by the patterning mask, of the barrier metal film.
A third aspect of the present invention is directed to a method of fabricating a semiconductor device by disposing metal wiring on the surface of an insulating film formed on a semiconductor substrate, comprising the steps of forming a recess in the insulating film; depositing a metal wiring film composed of a metal wiring material on the insulating film having the recess formed therein; selectively forming a polishing adjusting film in a depression occurring, opposite to the recess, on the surface of the deposited metal wiring film; and polishing the metal wiring film by chemical mechanical polishing after forming the polishing adjusting film.
According to the present invention, the polishing adjusting film is formed in the depression occurring on the surface of the metal wiring film, and processing using the chemical mechanical polishing is then performed. Therefore, in the chemical mechanical polishing processing, a surface plate pad for physically polishing the surface of the metal wiring film can be prevented from polishing in a state where a portion, corresponding to the recess, on the surface of the metal wiring film is depressed. Consequently, the metal wiring embedded in the recess in the insulating film can be prevented from being dished.
Consequently, it is possible to obtain good-quality metal wiring having a cross-sectional area and an electrical resistance which are equal to their designed or desired values.
The metal wiring can be prevented from being dished. When the method according to the present invention is applied to formation of multi-layer wiring, therefore, the unequality in the surface of a further insulating film on the insulating film and the metal wiring can be reduced. Accordingly, it is possible to reduce the possibility of defocusing at the exposure processing in a photolithographic process for patterning the further insulating film with a recess for embedding a further metal wiring. Further, it is possible to prevent the further metal wiring from being short-circuited by the metal wiring film remaining in a depression occurring in the further insulating film. Moreover, processing for flattening the further insulating film need not be additionally performed in order to prevent the defocusing and the short-circuit of the further metal wiring. Accordingly, the fabrication cost is not increased.
It is preferable that the step of selectively forming the polishing adjusting film comprises the step of applying a material for the polishing adjusting film to the depression, and the step of baking the applied material for the polishing adjusting film. According to this method, it is possible to selectively form the polishing adjusting film relatively simply without using a patterning technique and an etching technique.
It is preferable that the step of polishing the metal wiring film by the chemical mechanical polishing is terminated at the time point where a surface area outside the recess in the insulating film is exposed, that is, at the time point where the surface of the metal wiring film is almost flush with the surface, outside the recess, of the insulating film.
In the method according to the present invention, the step of laminating a barrier metal film on the insulating film having the recess formed therein may be further included between the step of forming the recess and the step of depositing the metal wiring film. In this case, it is preferable that the polishing adjusting film is a polishing rate adjusting film whose polishing rate by the chemical mechanical polishing is lower than that of the metal wiring film and is higher than that of the barrier metal film.
According to this method, by forming the polishing rate adjusting film in the depression occurring on the surface of the metal wiring film, it is possible to adjust the progress of the polishing in each portion on the surface area of the metal wiring film. Consequently, it is possible to prevent a portion, inside the recess, of the metal wiring film from being polished extra by the chemical mechanical polishing processing. Even when the barrier metal film is formed, therefore, the metal wiring can be satisfactorily prevented from being dished.
The polishing adjusting film may be formed using a material whose polishing rate by the chemical mechanical polishing is approximately equal to that of the metal wiring film.
A material whose polishing rate is approximately equal to that of the metal wiring film may be a metal wiring material of the same type as that of the metal wiring film.
As in this method, by forming the polishing adjusting film of the metal wiring material having a polishing rate approximately equal to that of the metal wiring film, the surface of the metal wiring film on which the polishing adjusting film has been laminated can be almost uniformly polished in the chemical mechanical polishing.
In this case, it is particularly preferable that the polishing adjusting film is formed such that the surface thereof is almost flush with the surface of the metal wiring film. By terminating the chemical mechanical polishing processing at the time point where the surface area outside the recess in the insulating film is exposed upon removal of an unnecessary portion of the metal wiring film, therefore, the surface, outside the recess, of the insulating film and the surface, inside the recess, of the metal wiring film can be made almost flush with each other.
When the polishing adjusting film is composed of the metal wiring material of the same type as that of the metal wiring film, the metal wiring film may be formed to such a thickness that the bottom surface of the depression is lower than the surface, outside the recess, of the insulating film. In this case, the polishing adjusting film remains on the surface of the metal wiring film at the time point where the surface, outside the recess, of the insulating film and the surface, inside the recess, of the metal wiring film are flush with each other. The metal wiring can be constructed by the remaining polishing adjusting film and the metal wiring film. In this case, the amount of the metal wiring material required to form the metal wiring film can be reduced, thereby making it possible to construct the semiconductor device at low cost.
The metal wiring film may be formed to such a thickness that the bottom surface of the depression is higher than the surface, outside the recess, of the insulating film. In this case, at the time of the chemical mechanical polishing processing, the polishing adjusting film formed in the depression can be completely removed.